An estimated 23 million Americans, including adolescents and the elderly, suffer from circadian rhythm sleep disorders, such as delayed sleep phase disorder, advanced sleep phase disorder and winter depression. These conditions are characterized by persistent insomnia and/or excessive daytime sleepiness, impaired performance, reduced well being and lower quality of life. The negative symptoms result from a misalignment between the timing of sleep and the internal circadian clock. Clinical research has demonstrated that circadian rhythm sleep disorders are most effectively diagnosed (differentiated from other causes of insomnia) and treated if each individual patient's circadian phase is known. The timing of the master internal circadian clock is most reliably measured from the onset of the endogenous circadian rhythm of melatonin, a neuroendocrine hormone, as measured in dim light (dim light melatonin onset, or DLMO). However to date the reliable and valid assessment of the DLMO is limited to the research laboratory setting. This application answers PAR-08-212 Methodology and Measurement in the Behavioral and Social Sciences which calls for research to improve and develop methodology and measurement in the behavioral sciences through innovations in data collection techniques and measurement...approaches that integrate behavioral science research with biological science research are particularly encouraged...developing and validating research instruments that fill a gap in research needs...improve measurement in the real-world setting. Our goal is to develop a streamlined procedure for the accurate assessment of circadian phase (DLMO) outside of the laboratory that will provide clinicians and researchers with a novel diagnostic and research tool. In this way the underlying neurobiological cause of a patient's insomnia and/or circadian rhythm disorder can more readily be diagnosed and treated. Specific Aim 1 is to validate procedures for at-home circadian phase assessment in a large sample of healthy people (n=120). Validation will occur by (1) objectively measuring compliance to the at-home procedures and (2) comparing DLMOs collected at home to DLMOs collected in the laboratory, in a within-subjects counterbalanced design. We have pilot data to support the validity of our at home procedures. Specific Aim 2 is to validate the same at home procedures in patients with delayed sleep phase disorder (n=30). Specific Aim 3 is to conduct rigorous analyses to inform future users which subject characteristics and light levels predict (1) compliance to the at home procedures and (2) valid at-home DLMOs. The results of this 3 year study will have substantial implications for the translation of basic and clinical research to the community: (1) the diagnosis and treatment of insomnia and circadian rhythm sleep disorders will be significantly enhanced, thus improving public health and safety, mood and quality of life, (2) community participation in research will be improved, particularly in vulnerable and under represented populations, thus increasing scientific knowledge and (3) research and clinical costs will be substantially reduced.